Atrial fibrillation is an irregular heart rhythm that adversely affects approximately 2.5 million people in the United States. It is believed that at least one-third of all atrial fibrillation originates near the ostium of the pulmonary veins. Anatomically, two pairs of pulmonary veins are connected to the left atrium of the heart with each pair delivering blood to the heart from one of the patient's lungs. It is further believed that the optimal technique to treat atrial fibrillation is to create circumferential lesions around the ostia where a pulmonary vein connects with the left atrium. More specifically, the goal is to ablate tissue to form a conduction block to thereby prohibit the transmission of irregular electrical signals that can cause an arrhythmia. To be effective, the conduction block must completely block irregular signals and this often requires the ablation of a relatively deep, uniform lesion.
Heretofore, due to the relatively large diameters of these ostia, cryoablation procedures have required multiple, successive contacts between the cryo-element and the tissue around the periphery of an ostium. More specifically, these procedures have required the cryo-element to be successively moved around the ostia to create a patchwork array of ablations. This often results in a non-uniform circumferential ablation that fails to form an adequate conduction block. Furthermore, when multiple, successive contacts are prescribed, special catheter structures are generally required to give a catheter the agility required to carefully move from one location to the next within the pulmonary vein. These structures increase the size of the distal end of the catheter, making the catheter harder to steer and navigate through the vasculature of the patient to the treatment site. In short, procedures requiring multiple contacts tend to be complicated, time consuming, difficult to perform, and are generally unreliable.
Another factor that must be considered when ablating internal tissue is the stability of the ablation element (e.g. cryo-element) relative to the target tissue. During ablation, movements of the patient such as heartbeats and breathing can cause the ablation element to move or bounce. Failure to prevent these movements of the ablation element relative to the target tissue can disrupt the flow of energy between the ablation element and the tissue resulting in a non-uniform ablation. As indicated above, non-uniform ablations often result in an ineffective conduction block.
In light of the above, it is an object of the present invention to provide systems and methods suitable for the purposes of cryoablating substantially circumferential ablations of internal tissue in a single step. It is another object of the present invention to provide systems and methods for forming conductive blocks to treat heart arrhythmias such as atrial fibrillation. It is yet another object of the present invention to provide systems and methods for cryoablating internal target tissue that can be performed quickly and are relatively reliable. Still another object of the present invention is to provide systems and methods for cryoablating circumferential ablation that are easy to use or perform and are comparatively cost effective.